We have recently discovered that oligodendrocyte-enriched preparations isolated from the mature central nervous system contain a small percentage of glial precursor cells, identified by the presence of the surface antigen ganglioside GD3. These GD3+ cells differentiate into astrocytes in culture. The properties of such glial precursor cells in neonatal rodent brain have been well described by others. The longterm objective of this project is to determine the differentiation pathways of these cells in the developing and mature nervous system. Viable cell preparations, containing a mixture of ooligodendrocytes, immature cells and precursor cells, will be isolated from rat brain at different ages of development, including adulthood. The glial precursor cells will be purified from mixed preparations by two strategies of immune selection. When the CD3+ cells are in the minority they will be purified by magnetic antibody techniques or by panning; when in the majority, mature oligodendrocytes will be destroyed complement lysis using anti-galactocerebroside antibodies. A subpopulation of bipotential glial progenitor cells, carrying the A2B5 surface antigen, will be purified from the GD3+ population by magnetic antibody techniques. The behavior and fate of all three types of cell preparations (mixed cultures, purified GD3+ cells, and purified A2B5+ cells) from animals of different ages will be defined in culture using quantitative immunocytochemical and morphological methods. By using double-labeling with an appropriate battery of antibodies to cell-specific antigens we will be able to describe the differentiation pathway of the precursors/progenitors (to oligodendrocytes or astrocytes), the percentage of cells that follow each lineage and the kinetics of differentiation. Attempts to influence the lineage selection, proliferation and differentiation of the precursors will employ agents such as PDGF, known to delay progenitor differentiation, and CNTF, known to induce astrocyte differentiation. Since in vitro studies describe only the potential repertoire of precursor cells, similar immunocytochemical studies will be applied to tissue sections of developing and mature rats to determine whether the lineage of precursor cells is the same in vivo as in vitro. The broad significance of this work is that glial precursor cells may not only furnish differentiated glia during development, but may serve as a reservoir of astrocytes for repair (reactive gliosis), and oligodendrocytes for remyelination in the adult.